The broad objective of this research is to examine the effects of state (Michigan) and federal legislation intended to reduce the relative cost of prescription drugs through the measurement of the substitution of lower-priced generically equivalent drugs for those brand name drugs prescribed by physicians. 1. For various time periods, analyze the factors affecting potential and actual rates of substitution of drug products. 2. Compare over time the relative importance of factors affecting substitution. 3. For various time periods, estimate the average retail price of various classes of prescriptions. 4. Compare over time the average retail price of classes of prescriptions. 5. For various time periods, analyze factors affecting the variation of retail prescription prices. 6. Compare over time the relative importance of factors affecting the variation of retail prescription prices. 7. Conduct a specific analysis of the effect of M.A.C. Regulations on the cost of prescriptions. In order to control for extraneous factors not associated with the process of substitution, a control state (Wisconsin) will be utilized in which legislation allowing substitution is not involved. The control state also will allow for comparison of effects of M.A.C. Regulations between states which allow or forbid drug product substitution. Data from which observations are to be made will be derived from a yearly systematic sample of approximately 800 to 1000 prescriptions each from a stratified random sample of between 100 and 130 pharmacies, representative of the regional, size and ownership variations of pharmacies in Michigan and the control state.